This invention pertains to thermosetting epoxy-polyamide coatings useful in industrial or maintenance coatings, and particularly to a method of stabilizing viscosity and sag resistance properties of such coatings during the catalyzed pot life thereof which is the period after the coating composition has been catalyzed by admixture of the epoxy resin component with the polyamide component. Polymide type coatings typically exhibit a sag problem after being applied to an upright or vertical surface substrate, which is not apparent in similar polyamine type coatings.
Prior art epoxy-polyamide compositions typically are stabilized with respect to sag resistance by the addition of fumed silica or certain clays. Such additives are known as thixotropic agents, including Cab-O-Sil.RTM. fumed silica and Bentone.RTM. clays, which are added to thicken the coatings mixture and impart thixotripic properties to the coatings. However, sag resistance of freshly catalyzed thermosetting coatings often decrease significantly over the entire catalyzed pot life of freshly converted or catalyzed epoxy-polyamide coatings. Typically, over 50% of the initial sag resistance is lost after only half of the catalyzed pot life. Other prior art compositions suggest the inclusion of ethylene glycol and/or glycerine to improve the stability of thermosetting epoxy-polyamide compositions containing fumed silica or clay thixotropic agents. However, only slightly improved sag resistance results along with highly detrimental viscosity increases. Illustrative comparative examples of these prior suggestions appear in the examples hereinafter.
The advantageous physical properties of thixotropic paints are ideally non-drip and splash characteristics, freedom from pigment settling, ease of brushing, and application of thick coats without danger of sagging.
It now has been found that the sag resistance of catalyzed thermosetting epoxy-polyamide compositions can be substantially improved without detrimental increase in viscosity over extended periods of catalyzed pot life by the inclusion of minor amounts of cationic stabilized material. The cationic stabilizing additive comprises a ethoxylated quaternary ammonium chloride salt and preferably added in amounts above 1.0% by weight of the epoxy-polyamide polymer solids. This cationic stabilizer advantageously provides stable post catalyzed sag resistance at a viscosity sufficiently low enough to obtain 75% volume solids at application viscosities. A further advantage of the cationic stabilizer pertains to pigmented compositions where the inclusion of certain pigments in conjunction with the cationic stabilizer of this invention can effectively eliminate the need for inorganic thixotropic agents such as Cab-O-Sil.RTM. fumed silica or Bentone.RTM. clays. Still a further advantage relating to the use of cationic stabilizers in accordance with this invention relates to negligible viscosity change or sag resistance over extended storage life of 4 months or more as well as very stabilized viscosity and sag resistance over normal pot lifes of the catalyzed mixtures in use. These and other advantages shall become more apparent by referring to the detailed description of the invention along with the illustrative examples.